This invention relates to an automatic photographic developing machine for developing photosensitive material such as photographic film.
An automatic photographic developing machine has a plurality of treating tanks arranged in a row and filled with different kinds of treating solutions such as a developing solution, a bleaching agent and a fixer. Photosensitive materials are developed by passing them one after another through racks immersed in the treating solutions in these treating tanks.
As shown in FIG. 6, a rack 40 in each tank has a feed mechanism 41 for feeding photosensitive materials. If the photosensitive materials are films, the feed mechanism 41 comprises a plurality of sprockets 42 which engage square holes formed in leaders to which the leading ends of films are connected to feed the leaders.
The sprockets 42 are rotated by transmitting the rotation of an input shaft 43 supported on the top of the rack 40 through a gear train 44. The input shaft 43 has a driving sprocket 45 adapted to mesh with a chain 47 provided on one side of the treating tank 46 near its top when the rack 40 is inserted in the treating tank 46. The sprocket 45 is thus rotated by moving the chain 47.
While photosensitive materials are being fed by the sprockets 42 in the rack 40, a force that tends to push up the rack 40 acts on the rack. If the rack 40 is pushed up by this force, the driving sprocket 45 will disengage from the chain 47, making it impossible to transmit turning torque from the chain 47 to the sprockets 42 and thus to feed photosensitive materials.
But if the rack 40 is fixed in position to completely prevent it from being pushed up, the gear of the gear train 44 in the feed mechanism 41 may be damaged by being rotated forcibly if the gear train 44 is put under excessive load e.g. due to clogging of a photosensitive material.
To prevent this problem, automatic developing machines are usually provided with a protective means that disengages the driving sprocket 45 from the chain 47 by pushing up the rack 40 only if an excessive load acts on the driving sprocket 45 meshing with the chain 47 or the gear train 44.
FIGS. 6 and 7 show a conventional protective means of this type. It has a guide plate 48 fixed in position on one side of the chain 47 and having a cutout 49 which can accept the end of the input shaft 43 supported on the rack 40.
The protective means further includes a slide plate 50 slidable on the top surface of the guide plate 48 and having a control piece 51 and a cutout 52 wider than the cutout 49. The cutout 52 is partially closed by the end of a presser plate 53 which is vertically movable along a pin 54 protruding from the slide plate 50 and is urged downward by a spring 55.
Normally, the spring-biased presser plate 53 keeps the driving sprocket 45 and thus the rack 40 from being pushed up. If an excessive load acts on the driving sprocket 45 or the gear train 44, the presser plate 53 is pushed up by the input shaft 43, so that the driving sprocket 45 will disengage from the chain 47.
The spring 55 used in such a conventional protective means has to be high in chemical resistance. Thus, its material cost tends to be high. Also, this protective means is made up of a rather large number of parts, and it is troublesome to assemble or replace broken parts.
An object of this invention is to provide an automatic photographic developing machine which allows each rack to be pushed up only if the feed mechanism of each rack is put under excessive load, and which is made up of fewer parts and thus simple in structure.